Farm update week of February 20th; Caring for the soil, part 2

Winter came back a bit since our last update, and limited the amount of work we could do. But things are supposed to warm up again by the end of the week.

We planted out first batch of peas, under a row cover and a plastic covered tunnel. The peas were pre-sprouted in a can of warm water. Pre-sprouting helps seeds to germinate if the soil temperature is too cool or warm. Once the seeds start growing, they will continue to do so even if the soil temperature is not optimal. We used lots of bent rebar pins hammered into the soil to hold down the tunnel, in the hope that it won’t blow away. But since our farm is in a particularly windy spot, we will have to wait and see. I still don’t have pictures of this, but I’ll get them up soon, if it works!

In my last post on caring for the soil, I mentioned that there is an excess of potassium in the soil. Organic matter typically contains a large amount of potassium in it relative to other elements; potassium is used to build the structure of plants, and thus materials such as wood chips, straw, and leaves contain a lot of potassium, while the other more mobile elements have been leached out or moved by the plant into roots and seeds. So adding organic matter to our soil will increase the relative imbalance of potassium. This is a problem, because organic matter is very important to soil health. It helps the soil form a good crumb structure, hold water and nutrients from leaching away, and most importantly, feeds the microorganisms, which protect and feed the plants. The more life there is in the soil, the better, and organic matter is the fuel for this life.

To add organic matter without unbalancing the soil, we will be growing lots of cover crops, particularly rye, sorghum, oats, and clover. These plants will loosen the soil, protect it from the sun and wind, and add organic matter to the soil when they decompose, all without adding any more potassium. This is also more sustainable then importing organic matter from other soils to their detriment. Legume cover crops, such as clover, vetch, and field peas, also fix nitrogen from the air with the help of symbiotic bacteria. Eventually, we hope to grow all our own nitrogen in this manner and avoid purchasing nitrogen fertilizer.

Avoiding the importation of organic matter will also help us avoid any potential contaminants. Recently, new herbicides have been developed that do not break down in the composting process; they can contaminate straw, manure, hay, and grass clippings, and when applied to a farm or garden, can inhibit the growth of broadleaf plants for as many as seven years.

We recently borrowed a broadfork to assess its performance on our farm. A broadfork is a larger version of the standard garden digging fork, with specially shaped long tines, a wide crossbar, and two handles. For pictures and video of a broadfork in action, here is a link to the version made by Valley Oak. I’m very happy with it; using it allowed us to loosen our hard soil a foot down, without the smearing and destruction of soil life and structure associated with tilling or plowing. Using it is also more enjoyable then using a tiller. Over time, the roots of the cover crops mentioned above will fill the soil voids produced by the broadfork, making the improvement permanent and creating a deep, rich topsoil.

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Caring for the Soil, Part 1

Ultimately, farmers are not in the business of raising crops; they are in the business of growing soil. Top soil is the beginning and end of farming. Soil is also an immensely complex system, varying from place to place, even over short distances, and containing a stunningly intricate system of life. Chemical, structural, and biological processes must all be fostered if a farmer wishes to improve his soil.

On our farm, the soil is a fairly heavy clay, which tends to be dense and sticky when wet and hard when dry. It has low organic matter and a slightly alkaline pH.

In a soil, the base cations,  (Calcium, Magnesium, Potassium, and Sodium) should be in a certain ratio; Calcium should take up the vast preponderance of the available “storage” (cations are stored on humus and clay particles) followed by magnesium, potassium, and sodium in that order. While Calcium can be as high as 70%, magnesium should be around 15%, and potassium should be a mere 2-5%. (Sodium should be always lower then potassium, and is not essential.) If these ratios are off, plant growth, soil life, and even soil texture will suffer.

It should be pointed out that this is just one of many different theories on soil health. Some farmers target other ratios, though always with Calcium taking the largest share. And many farmers don’t look at ratios at all; instead, they add a sufficient amount of each nutrient for the upcoming growing season. After much research, I’ve decided to follow the Albrechtian ratios as given above, since they were developed with a focus on the health of the whole system.

It is also important to realize that plants don’t “eat” as we do. There are a number of nutrients they need from the soil; Nitrogen, Phosphorus, Calcium, Magnesium, Potassium, Sulfur, Zinc, Copper, Iron, Manganese, and Boron are the most important. However, taken all together they make up a very small percent of a plant; most of the plant’s bulk is make of carbon, hydrogen, and oxygen drawn from the air and water.

In any case, if the chemistry of a soil is corrected, the soil will come to life biologically.

On our farm, the potassium is much too high. This is a complicated problem. For one thing, just like salt in soup, you can’t easily get a nutrient out of the soil. For another thing, most organic matter is high in potassium relative to the other nutrients it contains, so importing lots of organic matter will further imbalance this soil. The other cations are in fairly good shape. We are slowly resolving the problem by adding some gypsum every year. Gypsum a compound of sulfur and calcium. The calcium will replace the potassium, which will then combine with the sulfur to create potassium sulfate. Potassium sulfate is water soluble, so it will move deeper into the soil, away from the root zone. (The sulfur is also a necessary nutrient in the soil.)

Nitrogen is also necessary in fairly large amounts every year; but since it is fundamentally tied to the organic matter content of the soil, I will discuss it in the next post.

The soil started out with slight deficiencies in boron, copper, and zinc. These nutrients are tricky because they are needed in fairly small amounts, and an overdose can damage the soil. For instance, in the topsoil of a whole acre, there needs to be four pounds of boron; no more and no less. This translates into a tiny sprinkling of borax on each bed. These nutrients can not be added without careful soil testing.

In my next post, I will discuss our strategy for the organic matter and microbial life in the soil.